Polyalkylene glycol monomers, for example (meth)acrylic ester monomers obtainable by the esterification reaction of alkoxy (poly) alkylene glycols with an unsaturated monomer such as (meth)acrylic acid, and polyalkylene glycol monoalkenyl ether monomers such as unsaturated alcohol-alkylene oxide adducts, are of value as raw materials for the production of various polymers. Such polymers can suitably be used, for example, as cement additives (cement dispersants), pigment dispersants for dispersing calcium carbonate, carbon black, ink and the like, scaling inhibitors, dispersants for gypsum-water slurries, dispersants for coal-water slurries (CWM), thickening agents and like chemical products.
After the production of polyalkylene glycol monomers, they are generally stored and transferred before they are used as raw materials for polymer production. For example, they are stored for a while or for a fairly long time before use in polymer production or, when the plant for polyalkylene glycol monomer production is remote from the plant for polymer production, they are to be transferred. Thereafter, the polymerization step is carried out by adding the polyalkylene glycol monomer sequentially, to a polymerization reaction vessel.
When, however, a polyalkylene glycol monomer, which is generally used as a raw material for polymer production, occurs as a solid at ordinary temperature, it is melted by heating in using the same after storage and/or transfer. On that occasion, a gel-like matter is formed or, in the case of a (meth)acrylic ester monomer, it tends to be hydrolyzed or in the case of a polyalkylene glycol monoalkenyl ether monomer, it tends to be thermally decomposed. Furthermore, when a polyalkylene glycol monomer is stored and/or transferred in a heated and molten state, it may be oxidized, resulting, with high probability, in an increased peroxide value (POV) and gel-like matter formation in using the same. The reaction formula explaining the thermal decomposition of an unsaturated alcohol-alkylene oxide adduct and the reaction formula explaining the hydrolysis of a (meth)acrylic ester monomer are shown below by way of example as formulas (1) and (2):H2C═C(R)CH2CH2O(CH2CH2O)nH →H2C═CH(R)CH═CH2+HO(CH2CH2O)nH   (1)H2C═C(R)CO(OCH2CH2)nOCH3+H2O →H2C═C(R)COOH+H(OCH2CH2)nOCH3  (2)R: a hydrogen atom or a methyl group.
Such troubles occurring during storage and/or transfer of a polyalkylene glycol monomer result in a decreased purity or decreased quality because of increased impurity content in polymer production, hence a deterioration in quality or performance characteristics of the chemical product produced from such polymer. For example, in the case of a cement dispersant, it has effects to improve the flowability of a cement composition and, at the same time, to improve the strength and durability of hardened products. When, however, it is contaminated with impurities or the polymer is deteriorated in its performance characteristics or quality, the resulting hardened products, such as civil engineering or building structures, may show a lowered strength or durability, whereby such problems as decreased safety and/or increases in repairing cost may possibly be caused.
It is an object of the present invention, which has been made in view of the above-mentioned state of the art, to provide a storing and/or transferring method of a polyalkylene glycol monomer by which the gel-like matter formation and/or decomposition reaction can be satisfactorily inhibited and, as a result, troubles can be prevented from occurring in the production process and the performance characteristics or quality of various chemical products can be satisfactorily prevented from being deteriorated.